The present invention relates generally to display of electronic documents and, in particular, to a technique for efficiently performing pagination of such a document.
So-called electronic books are known in the art and are increasingly becoming a part of ordinary life. In an electronic book, documents are presented to a reader using a computer-based display device. Examples of such devices are the xe2x80x9cROCKET EBOOKxe2x80x9d device by NuvoMedia, Inc. and the xe2x80x9cSOFTBOOK READERxe2x80x9d device by Softbook Press, Inc. One aspect of printed books that may be desirable to replicate in electronic books is the use of consistently reproducible pages and page numbers. However, in the context of electronic documents, certain challenges exist in providing reproducible pages and page numbers to users of an electronic book. A particular problem is how to quickly provide accurate, reproducible pages and page numbers after a user has opened an electronic book to an essentially unknown location in the book. This problem is reflected in the fact that the xe2x80x9cROCKET EBOOKxe2x80x9d device currently does not support the use of page numbers.
The technique of background pagination is generally known in the art of electronic documents. Using this technique, a user may choose to view a selected portion of a document in paginated or print-preview form. While the user is viewing a selected portion of the document, the computer accesses the file storing the document, locates the beginning of the document and recalculates page boundaries going forward until it reaches the selected portion thereby determining a stable page. By keeping a running page count as new page boundaries are recalculated, a page number for the selected portion may also be determined. While this method works, it is processor-intensive and, for any document of significant length (such as a novel) is often likely to take a significant amount of time to complete.
Another solution is to include page information in the computer-readable file storing the document. Thus, along with the text and image data forming the content of the document, one would embed information indicative of page numbers at appropriate locations. However, the page number data embedded in this manner would no longer be accurate in the event that the document is re-formatted, for example, in response to a change in font size of the text. Further still, this implementation would make the format inflexible with respect to display of the document on different sized devices.
Thus, it would be advantageous to provide a technique for efficient determination of reproducible pages of electronic documents, particularly in response to a user opening a document to an otherwise unknown point in the document.
The present invention provides a technique for efficient pagination. As used herein, the term pagination refers to a process whereby reproducible pages are first determined, followed by the independent determination of page numbers in electronic documents (xe2x80x9cdocumentsxe2x80x9d). In the context of the present invention, a document encompasses all forms of electronically displayable information that require more than a single screen to be fully displayed. Pagination in accordance with the present invention is achieved through the use of a list or index of predetermined hard breaks within the document. When a user opens a document to a selected portion, the closest such hard break occurring before the selected portion is rapidly identified. A corresponding list or index of active formatting tags (such as HTML tags) applicable to content following the identified hard break is referenced to determine the proper layout for any intervening pages between the identified hard break and the selected portion, and possibly beyond the selected portion. In a preferred embodiment, at least a portion of the document subsequent to the selected portion is also formatted to ensure that the reproducible page has been acceptably and fully formatted. In this manner, a complete and reproducible page can be associated with the selected portion.
To determine the actual page number, the number of pages between hard breaks is also calculated and stored, possibly independently of the document""s file structure. Thus, a rolling sum of the number of pages between hard breaks is quickly calculated up to the hard break immediately prior to the selected portion. The final page number is thus the rolling sum plus the number of pages determined between the hard break and the reproducible page. In a preferred embodiment, the processing required to display the reproducible page is performed no later than the processing required to determine the page number. Using these techniques, the present invention allows pagination to be performed in an efficient and timely manner.